The present invention relates to a telephoto lens system of the inner focal type that is suitable for use with photographic cameras.
Large-aperture and telephoto type lenses are too heavy to handle easily, particularly when the lens system is advanced to a forward position. To avoid this problem, Japanese Patent Laid-Open Publication Nos. SHO 56-165110, 59-17519 and 62-235914, have proposed the use of inner focusing to achieve advanced lens positions.
However, the above-noted conventional lens systems experience large aberrational variations that occur when shooting objects at close range. These aberrations have been partly eliminated by the lens system described in Japanese Patent Laid-Open Publication No. SHO 62-235914. However, this system still experiences a disadvantageously short back focus or back focal length.
When using a telephoto lens system of the type used in the present invention, a rear conversion lens may be attached between the lens system and the camera body to increase the composite focal length. When this rear conversion lens is used, a longer back focus permits more satisfactory correction of the aberrations than offered in the overall system including in the rear conversion lens.